Effect of environmental conditions on growth of Alternaria alternata causing leaf blight of noni.

Effect of different pH levels, temperature, light intensity and media were tested against the growth of A. alternata under in vitro conditions. The results of experiment indicated that the growth of A. alternata was maximum in pH range of 6.00- 6.50 and temperature range of 25 - 30°C. The exposure of the fungus to alternate cycles of 12 hour light and 12 hour darkness resulted in the maximum mycelial growth of A. alternata compared to continuous light and dark. Among the different media tested, host leaf extract medium supported significantly the maximum growth of all the fifteen isolates of A. alternata followed by potato dextrose agar (PDA). Further, the cultural charecters viz., colony and substrate colour, margin, topography, zonation, pigmentation, colony diameter (mm) and sporulation varied among the isolates.